The manufacture of foams by extrusion foaming is known. However, known extrusion processes lead to relatively heavy and soft foam materials. Such foam materials are of limited utility for many applications, and are unsuited for applications where a high resistance to mechanical influences is required.
Light-weight foam materials prepared by extrusion foaming are disclosed by DE-AS 17 94 025. The foams disclosed by this reference are soft and flexible. One disadvantage associated with these foams lies in their inability to resist compression. Moreover, the method of preparation disclosed by the cited reference calls for the use of very large amounts of physical foaming agents. Thus, there are disadvantages associated with the properties of the foams disclosed by DE-AS 17 94 025, as well as with the method of foam preparation disclosed by this reference.
It is an object of this invention to provide a light-weight foam material which is also hard or brittle. Thus, the foams which are the subject of this invention combine the advantages of known light-weight foams such as polyolefin foams, with the desirable hard or brittle properties of other materials such as wood.